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><H1
CLASS="SECT1"
><A
NAME="RUNTIME-CONFIG-PRESET"
>18.15. Preset Options</A
></H1
><P
>     The following <SPAN
CLASS="QUOTE"
>"parameters"</SPAN
> are read-only, and are determined
     when <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> is compiled or when it is
     installed. As such, they have been excluded from the sample
     <TT
CLASS="FILENAME"
>postgresql.conf</TT
> file.  These options report
     various aspects of <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> behavior
     that might be of interest to certain applications, particularly
     administrative front-ends.
    </P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="GUC-BLOCK-SIZE"
></A
><TT
CLASS="VARNAME"
>block_size</TT
> (<TT
CLASS="TYPE"
>integer</TT
>)</DT
><DD
><P
>        Reports the size of a disk block.  It is determined by the value
        of <TT
CLASS="LITERAL"
>BLCKSZ</TT
> when building the server. The default
        value is 8192 bytes.  The meaning of some configuration
        variables (such as <A
HREF="runtime-config-resource.html#GUC-SHARED-BUFFERS"
>shared_buffers</A
>) is
        influenced by <TT
CLASS="VARNAME"
>block_size</TT
>. See <A
HREF="runtime-config-resource.html"
>Section 18.4</A
> for information.
       </P
></DD
><DT
><A
NAME="GUC-INTEGER-DATETIMES"
></A
><TT
CLASS="VARNAME"
>integer_datetimes</TT
> (<TT
CLASS="TYPE"
>boolean</TT
>)</DT
><DD
><P
>        Reports whether <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> was built with
        support for 64-bit-integer dates and times.  This can be
        disabled by configuring with <TT
CLASS="LITERAL"
>--disable-integer-datetimes</TT
>
        when building <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>.  The default value is
        <TT
CLASS="LITERAL"
>on</TT
>.
       </P
></DD
><DT
><A
NAME="GUC-LC-COLLATE"
></A
><TT
CLASS="VARNAME"
>lc_collate</TT
> (<TT
CLASS="TYPE"
>string</TT
>)</DT
><DD
><P
>        Reports the locale in which sorting of textual data is done.
        See <A
HREF="locale.html"
>Section 22.1</A
> for more information.
        This value is determined when a database is created.
       </P
></DD
><DT
><A
NAME="GUC-LC-CTYPE"
></A
><TT
CLASS="VARNAME"
>lc_ctype</TT
> (<TT
CLASS="TYPE"
>string</TT
>)</DT
><DD
><P
>        Reports the locale that determines character classifications.
        See <A
HREF="locale.html"
>Section 22.1</A
> for more information.
        This value is determined when a database is created.
        Ordinarily this will be the same as <TT
CLASS="VARNAME"
>lc_collate</TT
>,
        but for special applications it might be set differently.
       </P
></DD
><DT
><A
NAME="GUC-MAX-FUNCTION-ARGS"
></A
><TT
CLASS="VARNAME"
>max_function_args</TT
> (<TT
CLASS="TYPE"
>integer</TT
>)</DT
><DD
><P
>        Reports the maximum number of function arguments. It is determined by
        the value of <TT
CLASS="LITERAL"
>FUNC_MAX_ARGS</TT
> when building the server. The
        default value is 100 arguments.
       </P
></DD
><DT
><A
NAME="GUC-MAX-IDENTIFIER-LENGTH"
></A
><TT
CLASS="VARNAME"
>max_identifier_length</TT
> (<TT
CLASS="TYPE"
>integer</TT
>)</DT
><DD
><P
>        Reports the maximum identifier length. It is determined as one
        less than the value of <TT
CLASS="LITERAL"
>NAMEDATALEN</TT
> when building
        the server. The default value of <TT
CLASS="LITERAL"
>NAMEDATALEN</TT
> is
        64; therefore the default
        <TT
CLASS="VARNAME"
>max_identifier_length</TT
> is 63 bytes, which
        can be less than 63 characters when using multibyte encodings.
       </P
></DD
><DT
><A
NAME="GUC-MAX-INDEX-KEYS"
></A
><TT
CLASS="VARNAME"
>max_index_keys</TT
> (<TT
CLASS="TYPE"
>integer</TT
>)</DT
><DD
><P
>        Reports the maximum number of index keys. It is determined by
        the value of <TT
CLASS="LITERAL"
>INDEX_MAX_KEYS</TT
> when building the server. The
        default value is 32 keys.
       </P
></DD
><DT
><A
NAME="GUC-SEGMENT-SIZE"
></A
><TT
CLASS="VARNAME"
>segment_size</TT
> (<TT
CLASS="TYPE"
>integer</TT
>)</DT
><DD
><P
>        Reports the number of blocks (pages) that can be stored within a file
        segment.  It is determined by the value of <TT
CLASS="LITERAL"
>RELSEG_SIZE</TT
>
        when building the server.  The maximum size of a segment file in bytes
        is equal to <TT
CLASS="VARNAME"
>segment_size</TT
> multiplied by
        <TT
CLASS="VARNAME"
>block_size</TT
>; by default this is 1GB.
       </P
></DD
><DT
><A
NAME="GUC-SERVER-ENCODING"
></A
><TT
CLASS="VARNAME"
>server_encoding</TT
> (<TT
CLASS="TYPE"
>string</TT
>)</DT
><DD
><P
>        Reports the database encoding (character set).
        It is determined when the database is created.  Ordinarily,
        clients need only be concerned with the value of <A
HREF="runtime-config-client.html#GUC-CLIENT-ENCODING"
>client_encoding</A
>.
       </P
></DD
><DT
><A
NAME="GUC-SERVER-VERSION"
></A
><TT
CLASS="VARNAME"
>server_version</TT
> (<TT
CLASS="TYPE"
>string</TT
>)</DT
><DD
><P
>        Reports the version number of the server. It is determined by the
        value of <TT
CLASS="LITERAL"
>PG_VERSION</TT
> when building the server.
       </P
></DD
><DT
><A
NAME="GUC-SERVER-VERSION-NUM"
></A
><TT
CLASS="VARNAME"
>server_version_num</TT
> (<TT
CLASS="TYPE"
>integer</TT
>)</DT
><DD
><P
>        Reports the version number of the server as an integer. It is determined
        by the value of <TT
CLASS="LITERAL"
>PG_VERSION_NUM</TT
> when building the server.
       </P
></DD
><DT
><A
NAME="GUC-WAL-BLOCK-SIZE"
></A
><TT
CLASS="VARNAME"
>wal_block_size</TT
> (<TT
CLASS="TYPE"
>integer</TT
>)</DT
><DD
><P
>        Reports the size of a WAL disk block.  It is determined by the value
        of <TT
CLASS="LITERAL"
>XLOG_BLCKSZ</TT
> when building the server. The default value
        is 8192 bytes.
       </P
></DD
><DT
><A
NAME="GUC-WAL-SEGMENT-SIZE"
></A
><TT
CLASS="VARNAME"
>wal_segment_size</TT
> (<TT
CLASS="TYPE"
>integer</TT
>)</DT
><DD
><P
>        Reports the number of blocks (pages) in a WAL segment file.
        The total size of a WAL segment file in bytes is equal to
        <TT
CLASS="VARNAME"
>wal_segment_size</TT
> multiplied by <TT
CLASS="VARNAME"
>wal_block_size</TT
>;
        by default this is 16MB.  See <A
HREF="wal-configuration.html"
>Section 29.4</A
> for
        more information.
       </P
></DD
></DL
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